这项工作是由美国国家科学基金会成就奖CMMI-1350436以及科罗拉多州丹佛中心的大学教师发展的支持。作者要感谢江淮Corless，埃里克Losty和理查德·Wojcik他们在开发装置和模具对这些材料的合成与表征的帮助。作者还要感谢布兰登莽和Ellana泰勒材料的初步鉴定。

1.准备的液晶弹性体LCES <ol><li>加入4克4-双 - [4-（3- acryloyloxypropypropyloxy）苯甲酰氧〕-2-甲基苯（RM257）到30ml小瓶中。 RM257是二丙烯酸酯介晶和接收作为粉末。通过在热板上加入甲苯并加热到80℃的40重量％（即，1.6克）溶解RM257。这个过程通常需要不到5分钟，以溶解RM257成溶液。 注:其他溶剂可用于溶解RM257，如二氯甲烷（DCM），氯仿，二甲基甲酰胺这样的;然而，甲苯被选择，因为它允许单体固化在RT无反应期间快速具有溶剂蒸发，而DCM和氯仿可以在RT迅速蒸发的迈克尔加成反应完成之前。二甲基甲酰胺可以立即溶解RM257不需加热，但需要非常高的温度，以除去溶剂（〜150℃）。卡迈勒和公园用DCM组合和液晶，CB5，以溶解RM257。31 </li><li>冷却该溶液至室温。添加0.217克季戊四醇四（3-巯基丙酸酯）（PETMP），一个四官能的硫醇交联单体，和0.9157克的2,2-（亚乙二氧基）diethanethiol（EDDET），二硫醇单体。 PETMP和EDDET之间硫醇官能团的摩尔比为15:85。这个比率将被称作15摩尔％PETMP整个研究。 注意:如果在此过程中再结晶RM257，暂时放置在小瓶放回80℃的热板，直到单体返回到溶液中。在进行下一步骤之前，冷却该溶液至室温。 </li><li>溶解0.0257克（2-羟基乙氧基）-2-甲基苯（HHMP）的在溶液中。 HHMP是用于启用第二级光聚合反应的光引发剂。这个步骤可以如果第二级反应将不能利用被跳过。 </li><li>通过稀释丙胺制备催化剂的一个单独的溶液（DPA）用甲苯以1:50的比例。加入0.568克的稀释的催化剂溶液与单体溶液和剧烈混合在Vortex混合器。这对应于1摩尔％催化剂的相对于所述硫醇官能团。 注意:添加未稀释的催化剂，如DPA，向溶液可能会导致非常快速的局部聚合和将防止操纵聚合物溶液加入到在接下来的步骤中详述的期望的模具。 </li><li>放置在真空腔室中的单体溶液中1分钟，在508毫米汞柱以除去造成的混合的任何气泡。立即混合后执行此步骤。 </li><li>立即将溶液转移到所需的模子或喷射两种载玻片之间的溶液。模具应当由HDPE制造。模具不需要被覆盖，作为迈克尔加成反应是相对不敏感的氧气抑制。 </li><li>使反应进行至少12小时，在室温。该解决方案将开始凝胶W¯¯ithin在头30分钟。 </li><li>在真空室中在80℃下将样品和508毫米汞柱24小时以蒸发甲苯。一旦完成，该样品应当具有光泽的白色和不透明的外观在RT。 </li><li>重复定制四官能到二官能硫醇的单体的比例，在步骤1.2以25:75 50:50，和100的比率的过程:0。用于该研究的化学配方的详细表示于表1。 </li></ol>两阶段的反应的实时傅立叶变换红外2.动力学研究<ol><li>装备有MCT /乙检测器和XT-溴化钾束器的分光计。 </li><li>准备使用上述在使用0.5摩尔％的催化剂的相对于硫醇的官能团和光引发剂的0.5％（重量）的LCE部分的制备所概述的协议的混合物。两种引发剂分别测试，2-2二甲氧基-2-苯基苯乙酮（DMPA）和HHMP。 DMPA是一种更常用的我nitiator，而HHMP是在高温下更稳定。 </li><li>用玻璃吸管混合后立即将一滴氯化钠晶体之间LCE混合物。 </li><li>以2.92秒的采样间隔率记录的光谱。 </li><li>监视使用与SH吸收峰的峰高度轮廓的硫醇基团的转化率在2571厘米-1带的2614的基线-二千五百二十七-1。 </li><li>监视使用与C = C吸收峰的峰高度轮廓的丙烯酸酯基团的转化率在810厘米-1，829的基线- 781 -1。 </li><li>使反应FTIR下继续在RT直到硫醇峰高高原，表示硫醇基的转化率为100％。 </li><li>当硫醇基的完全转化，打开一个365nm的光源配有一个光导10分钟以完成过量的丙烯酸酯，在350毫瓦/厘米2的强度，其可以通过一个辐射计光度计来测量的聚合。 </li><li>监视丙烯酸酯基团的转化率如2.6所述。 </li></ol> 3.动态力学分析（DMA） <ol><li>通过喷雾幻灯片的表面具有疏水表面剂与擦用纸巾表面直到干燥制备两个载玻片。 </li><li>栈滑动在一起，使得它们被分离以1毫米间隔物。垫片可以用得分进行切割，并打破了单独的载玻片测量约25.4毫米×5毫米×1毫米。钳玻片一起使用，在两端的粘合剂剪辑。 </li><li>注射用玻璃吸管的幻灯片之间的单体溶液。这需要约1.5g所制备的单体溶液。 </li><li>使样品固化根据步骤1.7，至少12小时。分离载玻片，并干燥按照步骤1.8的样品。 </li><li>用剃刀刀片或剪刀，切割的矩形试验片具有30×10×1毫米3的尺寸。 </li><li>装载样品道具erly到DMA机器。测试在拉伸模式的样品，与有效长度测量10至15毫米。请注意不要过度拧紧把手上的试验样品，为0.1纳米往往是过多的扭矩拧紧交手时。 </li><li>周期将样品在0.2％的应变在-50 1赫兹到120℃以3℃/分钟的加热速率。将力轨道125％。 </li><li>测量在黄褐色∂曲线的峰值玻璃化转变温度 （Tg）。 </li><li>测量各向同性转变温度 （T i）和储能模量曲线的最低点。 </li><li>测量橡胶模量E&#39;R在T I + 30℃。 </li></ol> 4.应变对故障测试<ol><li>制备HDPE模具通过铣削ASTM V型狗骨腔以1mm的深度。 </li><li>用玻璃吸管，填充每个狗骨腔直至单体溶解液冲洗与模具的顶部。允许所述样本以按照步骤1.7和1.8固化并干燥。 </li><li>制备5从LCE样品拉伸试样配制的15变PETMP交联剂浓度，25，50，和100摩尔％。 </li><li>试样的计量长度内设置两块反射激光带5到7毫米。 </li><li>装入标本成机械测试仪配备激光引伸计，热室和500 N载荷传感器。使用自紧夹具固定的标本，如标本将逐出楔形夹具在高应变值。正确对齐激光引伸到跟踪长度的精​​确变化作为外加应变的函数。 </li><li>应变的试样在室温下用0.2毫米/秒的速度位移，直到失败。由试样的断裂限定的失败。 </li><li>的15摩尔％PETMP交联剂测试附加试样应变到故障测试作为温度的函数。试验样品在-40，-30，-20，-10，0，10，22，40，60，和80℃。容纳所有标本等温在所需的测试温度下10分钟，在测试之前。 </li></ol> 5.形状固定性和激励测试<ol><li>制备HDPE定制的狗骨模具为25毫米标距长度和1毫米×5毫米的截面积。 </li><li>根据步骤1.1至1.5制备15摩尔％PETMP单体溶液。 </li><li>使用玻璃吸管，填充每个模腔，直至单体溶液与模具顶部齐平。 </li><li>允许所述样本以按照步骤1.7和1.8固化并干燥。 </li><li>分开设置内试样的计量长度两块反射激光胶带5-7毫米。根据装载4.5步的样品。使用永久标记，在标记每一块反光带的另一侧上的点。记录点之间的长度。 </li><li>应变的试样在室温下用0.2毫米/秒的位移速率为100％，200％，300％，或400％的应变。 </li><li>在保持日Ë所需的应变水平，暴露样品到365纳米的紫外光源在强度〜10毫瓦/ 平方厘米10分钟，通过举办紫外灯从样品约150毫米。 </li><li>卸载样品，然后加热它上面T I诱导动作。允许样品冷却回至室温并记录点之间的长度。 </li><li>使用以下等式计算固定性: <img alt="式（1）" src="/files/ftp_upload/53546/53546eq1.jpg" width="500" /> 其中ε 施加之前编程应变光交联（通过激光引伸测量）和ε 固定是永久性变形的量后的光交联（通过点状位移的变化来衡量）。 </li><li>切从编程试样中心部30mm的长度的样品。 </li><li>正确装载样品到DMA测试仪。测试在拉伸模式的样品，与有效长度测量13至15毫米。确保不要过度收紧次Ë交手的试样。 </li><li>平衡下的0 N的预压的样品，在120℃冷却从120℃〜-25℃的样品以3℃/ min的速率。保持预力在0 N - 在整个测试。 </li></ol>

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作者什么都没有透露。

主链LCES已经研究了从执行器和传感器，以人造肌肉许多潜在的应用。不幸的是，合成和单畴对准仍然是防止这些应用中得到充分实现显著的挑战。11最近的工作探索了新的方法，以帮助克服这些挑战，例如使用可更换的交联，以便能够重新编程对准单畴多次本研究的33的目的是要提出一个相对未开发的方法来合成LCE和单畴使用两阶段TAMAP反应编程。第一级反应是基于使用的胺催化剂硫醇丙烯酸酯的迈克尔加成的"点击"的反应。由于该反应的性质，硫醇-丙烯酸酯的迈克尔加成反应的完全转化在5小时用DPA作为催化剂（图2）实现在RT。需要注意的是，这是重要的是与市售材料实现不经纯化和使用相对简单的"混合和倒"的方法。 0.5摩尔％的DPA相对于硫醇的官能团被选择在本研究为它给了聚合反应速率，从而允许将所述单体溶液注入模具中的控制。这是非常重要的是要注意，迈克尔加成的聚合速度仅由专用的催化剂浓度。高催化剂浓度的结果立即凝胶化与高单体转化率，其中太低催化剂浓度允许慢转换，并常常倍高的转化率不能达到甚至作为时间的函数。最终，聚合率可以通过催化剂浓度来调节。34其中一个这种方法提供的优点是，所得到的中间多畴LCE网络是均匀和稳定的，使得第二阶段反应可以无限期地延迟。这可使得合成和要在不同的实验室进行编程步骤。此外，第二阶段反应可以配上标准光刻技术来提供过光交联时空控制。25为了制备我们的实验样品，HHMP用作光引发剂，因为它的稳定性在可见光的存在，并在升高的温度下，使样品进行热循环应力驱动的启动或不触发引发形状记忆效应。一个独立的光引发剂用于本研究的FTIR部，有助于说明，这种方法有可能与各种自由基引发剂用于驱动第二阶段反应。 所提出的方法TAMAP提供简便地控制初始多畴LCE网络的结构。合成四LCE网络通过改变表明了广泛的可实现的热机械性能在PETMP交联剂和EDDET间隔之间的比率。在PETMP的浓度的增加破坏应变下降，而的 Tg和橡胶模量（E r）的增加与PETMP浓度的增加。此行为被解释为增加PETMP浓度增加了网络的交联密度和在网络内限制链的流动性。应变到故障行为如下的橡胶状弹性模量和破坏应变的内在反比关系如图其它无定形形状记忆聚合物（SMP）的网络。35 LCE系统具有高失败菌株通常更可取的，因为它们允许用于增加对准与较大的编程株单域。由谭∂的峰值测量我们的15％（摩尔）PETMP系统的破坏应变最大化，当接近的 Tg紧张。这也与以往的研究表明了maximu吻合米菌株在无定形的SMP网络玻璃化转变和 T 克的发作之间发生; 35,36然而，LCE样品不经历破坏应变迅速下降时Tg以上加热，如图大多数弹性体37这可以。归因于那件T G和T之间存在的高架谭∂ 区 I（ 即，向列相）。以前小组调查核实中向列LCE网络独特的棕褐色∂损失的行为。[38,39]这种损失的行为归因于软弹性的向列相，使得所述介晶的各向异性的形状可以容纳菌的轮流没有经历增加应力。 LCES已经产生了大量的科学兴趣的，由于其刺激响应形状变化的能力。40 </sup&gt;多畴LCE样品可以被编程以证明可逆应力驱动热传动如果拉伸下的恒定应力编程一个临时单畴（图4b-C）;然而，形状记忆效果，还可以实现在LCE网络。19,41在这项研究中，TAMAP合成LCE样品可以被编程为形状记忆在RT，其中一个显著的应变仍储存在样品中，即使该样品是Tg以上。以使无应力或"免提"致动，第二级光聚合反应可以被用来编程拉伸LCE样品处于永久对准单畴。第二阶段反应的效率可以通过测量固定性作为增加拉伸的函数进行检查。应当指出的是，固定性是用于评估的SMP网络的编程。42在这项研究中一个共同的度量，将样品程序性不同层次斯特拉的在（即，100％，200％，300％和400％）和显示出卓越固定性超过90％。我们的研究结果表明，按比例与编程应变热启动的大小是与链接增加了序参量增加机械驱动之前的结果一致。43例如，LCE样本进行了光固化在400％的应变表现出的平均115％的致动加热时和冷却％致动和207之间22和90℃时加热并在-25和120℃冷却。相对于其他的LCE研究，Ahir 等 44报道的LC聚合物纤维和400％的致动Yang等22报道了300％至400％的致动微型LCE支柱。要注意的是，本研究测量致动不同于许多LCE文献，这往往计算基于在各向同性状态的样品的长度的应变是非常重要的。在这项研究中，动应变总是基于或iginal长度合成的多畴样品。这是更适合于TAMAP方法，因为它提供了编程应变和光交联两个应变固定性及恢复对的效率的更有效的措施。无论如何，我们的报道动应变仍低于400％，所报告的其他研究。然而，这TAMAP反应仍相对未开发的和光交联的影响尚未完全被发现。而光交联是必要固定的永久单畴，过多光交联将防止致动的发生。理论上，不应存在光交联的最佳量既稳定单域，并允许最大驱动。总体而言，TAMAP方法提供了一个功能强大的工具来合成低碳经济体系，调整自己的结构，程序永久单畴排列，并最终探索这个迷人的一类材料。

LCES是一类刺激响应聚合物，其能够表现出应有的液晶（LC）顺序和橡胶弹性的组合的机械和光学功能的。这些材料可以显示出在形状上的刺激非凡的变化，软弹性行为，和可调谐光学性质，响应诸如热或光，1-3这使得它们适用于许多潜在的技术的应用，如人造肌肉，4,5-传感器，6和致动器。6,7- LCES已被证明在许多应用，如微夹持器为机器人，8微机电系统（MEMS），6,9-光栅装置，10可调孔径，6,11和微流体系统12 该产生有序的LC相的结构组件被称为介晶。介晶是液晶畴的基础和通常由两个或三个线性连接的芳环具有柔性末端。这些部分可以直接放置在该聚合物主链以创建主链LCES或作为侧基（即，侧或端上LCES）。1,13-主链LCES已经产生了很大的兴趣，因为它们4,14-17介晶秩序和聚合物主链构象之间的直接连接。这种直接耦合允许主链LCES表现出较高程度的介晶的取向，机械各向异性和应变动作。17 LCES的热传动依靠与LC顺序相关联的可逆各向异性各向同性转变。2要编程的LCE为致动，所述介晶必须首先沿一个导演定向以形成一个单畴（即，各向异性中间相），并通常被称为一个液体单晶弹性体。作为对准LCE在上述各向同性加热发生致动<html>结算温度 （T i）中，其中破坏了介晶的顺序到均质状态和驱动器的形状变化。甲单畴可以暂时通过施加外部应力（即，挂一重量）至样品，将对齐的聚合物链和定向介晶在应力的方向上而形成。可通过一个多步骤的过程，其涉及产生轻度交联的凝胶，随后通过机械应力的直接应用以诱导介晶的取向来实现的单磁畴的永久编程。一旦对准，继续反应至建立共价交联和稳定的单畴18其他 "一锅煮"对准技术可以在电场的存在下或通过表面取向中 （即，在玻片上摩擦聚酰亚胺）在聚合过程中。然而，这些方法通常限于薄膜样品。1,16 ntent"&gt; Finkelmann和贝格曼引入用于制备主链LCES第一合成路线使用二乙烯基介晶的和一步铂催化的氢化硅烷化反应中的四官能硅氧烷交联剂。15该方法已被广泛地适用于通过许多研究小组此外，以合成的主链LCES。17,19,20聚酯化和环氧基的反应也已被用于使主链LCES 21，所有这些方法都要求高纯度的原料和仔细的实验条件，以防止副反应。1这些方法依赖于无规交联的单体，导致定义不清的网络结构，因此，它更难以关联的结构，以LCES的属性。最近的研究已经使用点击化学作为工具来制备更均匀的LCE网络;然而，这些反应需要定制合成的起始介晶和硫醇的单体，其可以是具有挑战性的来生产，并且被限制以制备微米尺寸的致动器，而不是块状样品22-24 在LCES目前面临的挑战集中在如何开发是浅显的，重复性好，可扩展的设计定制LCE网络的可编程单畴合成方法。最近，我们的基介绍了两级硫醇-丙烯酸酯的迈克尔加成-光聚合（TAMAP）方法首次在介晶的系统来制备向列型主链LCES 25两阶段TAMAP反应形成双重固化聚合物网络，其中该聚合过程的分段允许聚合物结构的修饰两个不同的时间点。这一战略已经适应在过去的几年里设计和制造等先进材料，比介晶系统，如微执行器，26形状记忆聚合物，27,28和表面的皱纹等，29,30的TAMAP方法利用非stoichiometric组合物与过量的丙烯酸酯官能团。第一阶段反应是用于创建经由硫醇迈克尔加成反应，这是自限性的硫醇基的多畴LCES。这是中间LCE网络，将能够介晶域取向通过施加机械应力。从第一级迈克尔加成反应得到的多畴是无限期稳定的，并且单域的取向并不需要立即发生的反应完成后。过量的丙烯酸酯基团之间的第二级光聚合反应被用于永久固定对准的单畴和编程LCE为可逆的，无压力（即"免提"）致动。本研究的目的是探索和演示TAMAP反应的鲁棒性通过调查交联密度和在LCE系统的热力学的影响程序性菌株，制备主链LCES。我们展示了一个广泛的热属性和使用实现这一反应的驱动性能。

<table><tbody><tr><td>1,4-Bis-[4-(3-acryloyloxypropyloxy)benzoyloxy]-2-methylbenzene;&amp;nbsp; &lt;strong&gt;RM257&lt;/strong&gt;</td><td>Wilshire Technologies</td><td>174063-87-7</td><td>Di-Acrylate Mesogen&amp;nbsp;</td></tr><tr><td>2,2&amp;rsquo;-(Ethylenedioxy) diethanethiol;&amp;nbsp; &lt;strong&gt;EDDET&lt;/strong&gt;</td><td>Sigma Aldrich</td><td>465178</td><td>Di-Thiol Spacer&amp;nbsp;</td></tr><tr><td>Pentaerythritol tetrakis (3-mercaptopropionate); &lt;strong&gt;PETMP&lt;/strong&gt;</td><td>Sigma Aldrich</td><td>381462</td><td>Tetra-Thiol Crosslinker&amp;nbsp;</td></tr><tr><td>Dipropylamine; &lt;strong&gt;DPA&lt;/strong&gt;</td><td>Sigma Aldrich</td><td>D214752</td><td>Catalyst</td></tr><tr><td>2-Hydroxy-4&amp;prime;-(2-hydroxyethoxy)-2-methylpropiophenone; &lt;strong&gt;HHMP&lt;/strong&gt;</td><td>Sigma Aldrich</td><td>410896</td><td>Photoinitiator&amp;nbsp;</td></tr><tr><td>2-2-dimethoxy-2-phenylacetophenone; &lt;strong&gt;DMPA&lt;/strong&gt;</td><td>Sigma Aldrich</td><td>196118</td><td>Photoinitiator</td></tr><tr><td>Toluene</td><td>Sigma Aldrich</td><td>244511</td><td>Solvent&amp;nbsp;&amp;nbsp;</td></tr></tbody></table>

synthesis of programmable main-chain liquid-crystalline elastomers using a two-stage thiol-acrylate reaction

这项研究提出了一种新的两级巯基丙烯酸酯Michael加成，光聚合（TAMAP）反应制备主链液晶弹性体（LCES）用浅显的控制网络结构的对准单畴和编程。合成定制LCE网络被使用市售的常规混合原料和浇注的单体溶液注入模具以固化。初始多畴LCE网络经由自限硫醇丙烯酸迈克尔加成反应形成的。应变到故障和玻璃化转变行为进行了研究作为交联单体，季戊四醇四（3-巯基丙酸酯）（PETMP）的功能。的15摩尔％PETMP硫醇基，例如非化学计量系统和过量的15％（摩尔）的丙烯酸酯基团被用于证明该材料的健壮本质。该LCE形成的取向和透明的单畴拉伸时，有超过600％的最大破坏应变。拉伸LCE样品能够证明这两种应力驱动热传动当下一个恒定偏压应力或形状记忆效应保持拉伸和卸载时。甲永久性编程单畴是通过过量的丙烯酸酯基团的第二级光聚合反应时所获得的样品是在拉伸状态。 LCE样品光固化，并在100％，200％，300％和400％应变编程，所有样品显示出90％以上的形状固定性卸载时。总无压力致动的幅度从35％上升到115％更多的节目应变。总体而言，两级TAMAP方法是作为一种强大的工具，制备主链LCE系统并探究这些迷人刺激敏感材料结构 - 性能 - 性能关系。

在这项研究中，两阶段TAMAP反应固化动力学采用实时FTIR研究。上硫醇和丙烯酸酯基团的转化率作为时间的函数的一个系列FTIR研究同时捕获反应的阶段实施，并归一化结 ​​果示于图2A中。第一级硫醇丙烯酸迈克尔加成反应是通过用DPA如在交联聚合物网络的形成的催化剂和结果碱催化引发。在该初始反应结束，硫醇官能团达到接近100％的转化率在5小时的环境条件（〜22℃）下的，而在相同条件下70％之间达到78％的转化率的丙烯酸酯基团。硫醇 - 丙烯酸酯的迈克尔加成&#39;点击&#39;反应是自限性的，可以基于f的相对比率一个逐步增长，交联的，稳定的网络中的一个轻便的方式unctional群体存在。随后，第二阶段的光聚合反应，通过暴露于紫外线照射发起和网络内本剩余的未反应的丙烯酸酯基团是进一步交联以达到接近100％的最终的丙烯酸酯官能团转化。两个光引发剂，HHMP和DMPA及它们的反应动力学进行了研究，这些聚合物网络内，并且都见于第二阶段聚合反应结束时，以有效地创建交联的丙烯酸酯网络。丙烯酸酯基团作为曝光的强度的函数的转化率也进行了研究，并看到关联。总体而言，有人指出，虽然许多变量例如光引发剂和曝光时间可以变化，这是能够有效地实现高的最终的丙烯酸酯的转化率在第二级的内甚至用UV相对低水平10分钟结束强度（〜10-25毫瓦/厘米2相比350毫瓦/厘米2）。 图2B表示在3个不同的时间点，0，300，和320分钟的两阶段反应的FTIR吸收光谱。在时间0时，初始光谱同时捕捉硫醇和丙烯酸酯的官能团在其未反应的状态存在。在300分钟的时间点，由第一阶段的硫醇 - 迈克尔加成反应结束时，硫醇和丙烯酸酯峰高度被认为是降低了显着，从而意味着硫醇和丙烯酸酯的官能团已经进展到完成之间的反应。硫醇峰测量为接近100％的转化率在这一点上，而丙烯酸酯被认为要消耗高达78％。硫醇峰完全消失没有观察到，很可能从第一阶段反应的硫醇迈克尔加合物的存在被认为出现和与硫醇峰二千五百七十一-1重叠。在通过紫外线照射引发第二级光聚合反应结束，在320分钟点时，丙烯酸酯共n版本被看作是进行完全，这意味着在网络内剩余的丙烯酸类双键的转化率为100％。32 两级TAMAP方法提供了便捷的控制，探讨在LCES结构与性能的关系。上的应力-应变行为的交联密度的影响示于图3A。模量和断裂应力被证明能增加而增加PETMP内容，同时失效应变的增加而降低PETMP内容（图3B）。 LCE样品50和100％（摩尔）PETMP证明初始弹性加载之后的应力高原，由于链排列急剧增加的压力。相比较而言，用15和25％（摩尔）PETMP样品似乎表明更传统的弹性体装载随后由于链取向的增加的压力。所有测试的标本显示由白色不透明转变为清晰的透明度时stret高等教育委员会（ 图3E）。应当指出的是，所有样品保持很大程度的永久应变的骨折之后，没有恢复到在RT其原来的形状;然而，所有的样品在视觉上在加热时上述T I恢复到原来的形状。温度对失效应变的影响，然后研究了15摩尔％PETMP组合物（图3C）。在玻璃态，LCE标本展出脆败，没有明显的变形。在玻璃化转变的开始，破坏应变显著增加和随后的正切δ函数的度量以DMA的一般形状。破坏应变在10℃下达到最大值650％应变。为四LCE网络系统代表玻璃化转变行为示于图3D。所有LCE网络的同时显示在储能模量和正切δ曲线的非传统行为。的储能模量LL LCE网络显示出与众不同的最低限度是大致与T I相关。该正切δ功能是由一个初始峰随后升高的区域是减少，因为将样品加热到各向同性状态（有代表性的曲线可在图3C中可以看到）表示。对于四LCE系统进行测试，这两个的 Tg 和橡胶状弹性模量的增加而增加的交联密度。四个LCE系统的热机械性能的总结可以看出，在表2中。 LCES提供展示两个形状记忆效应和可逆致动（图4）的能力。 15摩尔％PETMP的未对齐的多畴试样用来说明不同形状切换路径，它们可以被编程到材料（图4A）。可逆压力驱动的启动是恶魔由通路图4A-BC的trated。该多畴样品挂一个60.6万重量施加恒定压力捉襟见肘。此偏压应力机械取向的介晶成透明单畴。当在冷却到低于T I加热到各向同性状态，并拉长的样本合同。这个过程可以无限重复。从试样除去当冷却低于 T i到 22℃下，这仍然是18℃的Tg以上的偏压应力时形状记忆效应是展出。虽然观察到一些弹性回缩，大多数菌株仍编入材料。应当指出的是，介晶保持在一个稳定的单畴取向，并且在其中夹持附着样品的自由端内的光学特性的显着的差异（即，所述把持部保持光泽的白色）。暖气日Ë样品上方T I激活满形状恢复，表明形状记忆周期如下图4A-BDE的通路，第二级光聚合反应可以被用来实现无压力致动，而不需要一个恒定偏压应力或周期之间的编程步骤。所述暂时对准试样是光固化用365nm的光在〜10毫瓦/ cm 2的10分钟（ 图4F）。样品经历了最小的弹性回缩时，由于过量的未反应丙烯酸酯基（ 图4G）之间建立共价交联的卸载。无压力的驱动，然后通过控制有关T使用 我在图 4G-H可逆途径的活化温度;然而，应当指出的是，样品不经历完全恢复回试样的初始形状。 （即，应变光聚合过程中）的影响作为固定性和致动为15摩尔％PETMP系统的函数示于图5A。所有样品显示出固定性值高于90％。编程应变的量并没有显着影响的固定性值在本研究中测试的应变范围。相反地​​，致动应变线性增​​加编程应变的量。平均来说，致动应变对应于编程应变值的大约30％。示出的致动作为温度的函数的代表性曲线可以看出，在图5B中 。应当指出的是，图5A中的致动应变值对应于测量室温之间，22℃，90℃， 而在图4B中所示的行为在-25和120℃监测。这种扩展温度范围内引起了dditional驱动应变得以实现:80％，102％，125％及207％应变致动在100％，200％，300％的样品编程，和400％的应变，分别。 <img alt="图1" src="/files/ftp_upload/53546/53546fig1highres.jpg" width="700" /> 图1.示意图单畴编程经由两级硫醇丙烯酸酯反应（A） 的 A二丙烯酸酯介晶（1,4-双- [4-（3- acryloyloxypropyloxy）苯甲酰氧〕-2-甲基苯- RM 257），二硫醇柔性间隔物（2,20-（亚乙二氧基）diethanethiol - EDDET），和四官能硫醇交联剂（季戊四醇四（3-巯基丙酸酯） - PETMP）被选定为可商购的单体。非等摩尔单体溶液制备，用过量15摩尔％的丙烯酸酯官能团，并允许经由迈克尔加成反应进行反应。二丙胺（DPA）和（2-羟基乙氧基）-2-甲基苯（HHMP）为广告DED作为各催化剂和光引发剂的溶液。 （B）经由迈克尔加成（第一阶段）具有均匀交联密度和潜过量的丙烯酸酯官能基团的代表性多畴结构的形式。 （C）上形成的机械应力被施加到多畴样品来定向介晶到临时单畴。 （D）光聚合反应（第二阶段）用于建立过量丙烯酸酯基团之间的交联，稳定样品的单域。 <a href="https://www.jove.com/files/ftp_upload/53546/53546fig1highres.jpg" target="_blank">请点击此处查看该图的放大版本。</a> <img alt="图2" src="/files/ftp_upload/53546/53546fig2highres.jpg" width="700" /> 图2. Michael加成反应，带有实时FTIR（A）动力学研究。代表两载物台Thiol - 丙烯酸酯反应动力学表示变换作为时间使用DMPA光引发剂的功能。在第一阶段结束时，硫醇基接近100％的转化率达到而丙烯酸酯基团的22％是未反应的。在第二阶段结束时，未反应的丙烯酸酯达到100％的转化率。 （二）红外吸收光谱显示固化时间为0时，第一阶段完成后，在300分钟前的巯基和丙烯酸酯的转换，并在320分钟的第二阶段完成后， <a href="https://www.jove.com/files/ftp_upload/53546/53546fig2highres.jpg" target="_blank">请点击此处查看该图的放大版本。 。</a> <img alt="图3" src="/files/ftp_upload/53546/53546fig3highres.jpg" width="700" /> 图3.热力学性质TAMAP LCE系统学报。（A）与15摩尔％过量的丙烯酸酯和不同代表应变到失败4 LCE系统的曲线量PETMP交联剂。 （B）的失效菌株作为PETMP交联剂的功能。 （C）温度对破坏应变为LCE系统与15％（摩尔）PETMP的影响。破坏应变进行比较一起利用DMA测得的材料的黄褐色∂功能。 （ 四）测试了4低碳经济体系的代表性玻璃化转变行为。拉伸LCE标本用15％（摩尔）PETMP相比，未经检验的标本（E）的图像。在（B）和 （C）误差条表示标准偏差。 <a href="https://www.jove.com/files/ftp_upload/53546/53546fig3highres.jpg" target="_blank">请点击此处查看该图的放大版本。</a> <img alt="图4" src="/files/ftp_upload/53546/53546fig4highres.jpg" width="700" /> 图4.形状切换在低碳经济之路。这示意代表多个二可fferent途径来实现形状的开关在LCES。 15％（摩尔）PETMP的自定义狗骨样品是用在这个演示用（A）的初步形成。可逆应力驱动的启动是通过调整温度大约 Tp实现（BC）i之间，同时在一个恒定的偏置力（60.6 MN）;形状记忆效果是通过以下的（ABDE）的编程和回收循环实现;与无压力的致动可以进行热处理（GH）之间的永久单畴已经被编程到在步骤样本（F）的后激活。图例说明液晶原方位多畴，单畴和各向同性的状态:T &lt;T i和 T&gt; T I图像拍摄于22和90℃，分别<a href="https://www.jove.com/files/ftp_upload/53546/53546fig4highres.jpg" target="_blank">请点击</a>这里查看该图的放大版本。 <img alt="图5" src="/files/ftp_upload/53546/53546fig5highres.jpg" width="700" /> 图5.热机械反应的编程了单畴LCE 系统 :（a）形状固定性代表永久对准单畴的效率，所有样品都显示90％以上固定性。致动的幅度之间22和90℃下测得的热板上。误差棒代表标准偏差。 （二）启动DMA上测量为-25〜120℃，工作状态随应用编程应变增加的幅度。 <a href="https://www.jove.com/files/ftp_upload/53546/53546fig5highres.jpg" target="_blank">请点击此处查看该图的放大版本。</a> <table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always"><tbody><tr><td> 名称 </strong&gt;的</td><td> RM 257（G） </td><td> 甲苯（G） </td><td> PETMP（G） </td><td> EDDET（G） </td><td> HHMP（G） </td><td> DPA（G）* </td></tr><tr><td> 15摩尔％PETMP </td><td> 4 </td><td> 1.6 </td><td> 0.2166 </td><td> 0.9157 </td><td> 0.0272 </td><td> 0.5681 </td></tr><tr><td> 25摩尔％PETMP </td><td> 4 </td><td> 1.6 </td><td> 0.3610 </td><td> 0.8080 </td><td> 0.0272 </td><td> 0.5681 </td></tr><tr><td> 50摩尔％PETMP </td><td> 4 </td><td> 1.6 </td><td> 0.7219 </td><td> 0.5386 </td><td> 0.0272 </td><td> 0.5681 </td></tr><tr><td> 100摩尔％PETMP </td><td> 4 </td><td> 1.6 </td><td> 1.4438 </td><td> 0.0000 </td><td> 0.0272 </td><td> 0.5681 </td></tr><tr><td colspan="7"> * DPA是在1:50比例稀释在甲苯中。 </td></tr></tbody></table>="1"&gt;表1.化学制剂LCE系统。在该研究中使用了四种不同的LCE系统。命名惯例是基于PETMP和EDDET之间硫醇官能团的摩尔比。所有系统都过量15摩尔％的丙烯酸酯官能团。应当指出，红外光谱研究中测试HHMP以及DMPA作为光引发剂，并减少了量的DPA催化剂一半，以帮助与动力学鉴定。 * DPA被以1:50的比例稀释在甲苯中。 <table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always"><tbody><tr><td> 名称 </td><td> T起始（℃） </td><td> 的Tg（℃） </td><td> 的Ti（℃） </td><td> E&#39;R（兆帕） </td></tr><tr><td> 15摩尔％PETMP </td><td> -6±2 </td><td> 3±1 </td><td> 62±3 </td><td> 0.18±0.01 </td></tr><tr><tD&gt; 25％（摩尔）PETMP </td><td> 0±2 </td><td> 7±1 </td><td> 76±2 </td><td> 0.47±0.05 </td></tr><tr><td> 50摩尔％PETMP </td><td> 8±2 </td><td> 16±2 </td><td> 78±1 </td><td> 0.78±0.13 </td></tr><tr><td> 100摩尔％PETMP </td><td> 15±1 </td><td> 27±1 </td><td> 64±3 </td><td> 1.90±0.13 </td></tr></tbody></table> LCE系统热机械性能的 表2中 总结。动态力学分析（DMA）测试显示了通过第一级迈克尔加成反应形成的初始多畴LCE网络的热机械性能。两个T I 和 E 为 &#39;r分别测量储能模量-温度曲线的最低点。

Watch this Scientific Journal Video about Synthesis of Programmable Main-chain Liquid-crystalline Elastomers Using a Two-stage Thiol-acrylate Reaction at JoVE.com

Synthesis of Programmable Main-chain Liquid-crystalline Elastomers Using a Two-stage Thiol-acrylate Reaction

一种新颖的方法，提出综合和使用市售的原料单体项目主链液晶弹性体。广泛热机械性能的混合物，通过调整交联剂的量量身定做，而启动性能是依赖于外加应变的编程期间的量。

的可编程主链液晶性弹性体用双级硫醇丙烯酸酯反应合成

This study presents a novel two-stage thiol-acrylate Michael addition-photopolymerization (TAMAP) reaction to prepare main-chain liquid-crystalline ...

synthesis-programmable-main-chain-liquid-crystalline-elastomers-using

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21.4K 次观看.  University of Colorado Denver. 一种新颖的方法，提出综合和使用市售的原料单体项目主链液晶弹性体。广泛热机械性能的混合物，通过调整交联剂的量量身定做，而启动性能是依赖于外加应变的编程期间的量。 

视频: Synthesis of Programmable Main-chain Liquid-crystalline Elastomers Using a Two-stage Thiol-acrylate Reaction

Preparation and Use of Samarium Diiodide (SmI2) in Organic Synthesis: The Mechanistic Role of HMPA and Ni(II) Salts in the Samarium Barbier Reaction

Although initially considered an esoteric reagent, SmI2 has become a common tool for synthetic organic chemists. SmI2 is generated through the addition of molecular iodine to samarium metal in THF.1,2-3 It is a mild and selective single electron reductant and its versatility is a result of its ability to initiate a wide range of reductions including C-C bond-forming and cascade or sequential reactions. SmI2 can reduce a variety of functional groups including sulfoxides and sulfones, phosphine oxides, epoxides, alkyl and aryl halides, carbonyls, and conjugated double bonds.2-12 One of the fascinating features of SmI-2-mediated reactions is the ability to manipulate the outcome of reactions through the selective use of cosolvents or additives. In most instances, additives are essential in controlling the rate of reduction and the chemo- or stereoselectivity of reactions.13-14 Additives commonly utilized to fine tune the reactivity of SmI2 can be classified into three major groups: (1) Lewis bases (HMPA, other electron-donor ligands, chelating ethers, etc.), (2) proton sources (alcohols, water etc.), and (3) inorganic additives (Ni(acac)2, FeCl3, etc).3
Understanding the mechanism of SmI2 reactions and the role of the additives enables utilization of the full potential of the reagent in organic synthesis. The Sm-Barbier reaction is chosen to illustrate the synthetic importance and mechanistic role of two common additives: HMPA and Ni(II) in this reaction. The Sm-Barbier reaction is similar to the traditional Grignard reaction with the only difference being that the alkyl halide, carbonyl, and Sm reductant are mixed simultaneously in one pot.1,15 Examples of Sm-mediated Barbier reactions with a range of coupling partners have been reported,1,3,7,10,12 and have been utilized in key steps of the synthesis of large natural products.16,17 Previous studies on the effect of additives on SmI2 reactions have shown that HMPA enhances the reduction potential of SmI2 by coordinating to the samarium metal center, producing a more powerful,13-14,18 sterically encumbered reductant19-21 and in some cases playing an integral role in post electron-transfer steps facilitating subsequent bond-forming events.22 In the Sm-Barbier reaction, HMPA has been shown to additionally activate the alkyl halide by forming a complex in a pre-equilibrium step.23
Ni(II) salts are a catalytic additive used frequently in Sm-mediated transformations.24-27 Though critical for success, the mechanistic role of Ni(II) was not known in these reactions. Recently it has been shown that SmI2 reduces Ni(II) to Ni(0), and the reaction is then carried out through organometallic Ni(0) chemistry.28
These mechanistic studies highlight that although the same Barbier product is obtained, the use of different additives in the SmI2 reaction drastically alters the mechanistic pathway of the reaction. The protocol for running these SmI2-initiated reactions is described.

Preparation and Use of Samarium Diiodide SmI2 in Organic Synthesis: The Mechanistic Role of HMPA and NiII Salts in the Samarium Barbier Reaction

A straightforward procedure for the preparation of samarium diiodide (SmI2) in THF is described. The role of two main additives namely hexamethylphosphoramide (HMPA) and Ni(acac)2 in Sm mediated reactions is demonstrated in the Sm-Barbier reaction.

二碘化钐的制备和使用（SMI<sub&gt; 2</sub&gt;）在有机合成中:HMPA和镍（II）盐的钐巴尔比耶反应的机理作用

Although initially considered an esoteric reagent, SmI2 has become a common tool for synthetic organic chemists. SmI2 is generated through the addition of ...

科研

化学

Amide Coupling Reaction for the Synthesis of Bispyridine-based Ligands and Their Complexation to Platinum as Dinuclear Anticancer Agents

Amide coupling reactions can be used to synthesize bispyridine-based ligands for use as bridging linkers in multinuclear platinum anticancer drugs. Isonicotinic acid, or its derivatives, are coupled to variable length diaminoalkane chains under an inert atmosphere in anhydrous DMF or DMSO with the use of a weak base, triethylamine, and a coupling agent, 1-propylphosphonic anhydride. The products precipitate from solution upon formation or can be precipitated by the addition of water. If desired, the ligands can be further purified by recrystallization from hot water. Dinuclear platinum complex synthesis using the bispyridine ligands is done in hot water using transplatin. The most informative of the chemical characterization techniques to determine the structure and gross purity of both the bispyridine ligands and the final platinum complexes is 1H NMR with particular analysis of the aromatic region of the spectra (7-9 ppm). The platinum complexes have potential application as anticancer agents and the synthesis method can be modified to produce trinuclear and other multinuclear complexes with different hydrogen bonding functionality in the bridging ligand.

This protocol describes the use of amide coupling reactions of isonicotinic acid and diaminoalkanes to form bridging ligands suitable for use in the synthesis of multinuclear platinum complexes, which combine aspects of the anticancer drugs BBR3464 and picoplatin.

酰胺偶联反应为双吡啶基配体及其络合合成，以白金为双核抗癌药物

Amide coupling reactions can be used to synthesize bispyridine-based ligands for use as bridging linkers in multinuclear platinum anticancer drugs. ...

The Preparation and Properties of Thermo-reversibly Cross-linked Rubber Via Diels-Alder Chemistry

A method for using Diels Alder thermo-reversible chemistry as cross-linking tool for rubber products is demonstrated. In this work, a commercial ethylene-propylene rubber, grafted with maleic anhydride, is thermo-reversibly cross-linked in two steps. The pending anhydride moieties are first modified with furfurylamine to graft furan groups to the rubber backbone. These pendant furan groups are then cross-linked with a bis-maleimide via a Diels-Alder coupling reaction. Both reactions can be performed under a broad range of experimental conditions and can easily be applied on a large scale. The material properties of the resulting Diels-Alder cross-linked rubbers are similar to a peroxide-cured ethylene/propylene/diene rubber (EPDM) reference. The cross-links break at elevated temperatures (&#62; 150 &#176;C) via the retro-Diels-Alder reaction and can be reformed by thermal annealing at lower temperatures (50-70 &#176;C). Reversibility of the system was proven with infrared spectroscopy, solubility tests and mechanical properties. Recyclability of the material was also shown in a practical way, i.e., by cutting a cross-linked sample into small parts and compression molding them into new samples displaying comparable mechanical properties, which is not possible for conventionally cross-linked rubbers.

A simple two-step approach involving rubber modification and cross-linking yields fully reworkable, elastic rubber products.

热可逆交联橡胶通过的Diels-Alder反应的化学制备与性能

A method for using Diels Alder thermo-reversible chemistry as cross-linking tool for rubber products is demonstrated. In this work, a commercial ...

Constructing Thioether/Vinyl Sulfide-tethered Helical Peptides Via Photo-induced Thiol-ene/yne Hydrothiolation

Here, we describe a detailed protocol for the preparation of thioether-tethered peptides using on-resin intramolecular/intermolecular thiol-ene hydrothiolation. In addition, this protocol describes the preparation of vinyl-sulfide-tethered peptides using in-solution intramolecular thiol-yne hydrothiolation between amino acids that possess alkene/alkyne side chains and cysteine residues at i, i+4 positions. Linear peptides were synthesized using a standard Fmoc-based solid-phase peptide synthesis (SPPS). Thiol-ene hydrothiolation is carried out using either an intramolecular thio-ene reaction or an intermolecular thio-ene reaction, depending on the peptide length. In this research, an intramolecular thio-ene reaction is carried out in the case of shorter peptides using on-resin deprotection of the trityl groups of cysteine residues following the complete synthesis of the linear peptide. The resin is then set to UV irradiation using photoinitiator 4-methoxyacetophenone (MAP) and 2-hydroxy-1-[4-(2-hydroxyethoxy)-phenyl]-2-methyl-1-propanone (MMP). The intermolecular thiol-ene reaction is carried out by dissolving Fmoc-Cys-OH in an N,N-dimethylformamide (DMF) solvent. This is then reacted with the peptide using the alkene-bearing residue on resin. After that, the macrolactamization is carried out using benzotriazole-1-yl-oxytripyrrolidinophosphonium hexafluorophosphate (PyBop), 1-hydroxybenzotriazole (HoBt), and 4-Methylmorpholine (NMM) as activation reagents on the resin. Following the macrolactamization, the peptide synthesis is continued using standard SPPS. In the case of the thio-yne hydrothiolation, the linear peptide is cleaved from the resin, dried, and subsequently dissolved in degassed DMF. This is then irradiated using UV light with photoinitiator 2,2-dimethoxy-2-phenylacetophenone (DMPA). Following the reaction, DMF is evaporated and the crude residue is precipitated and purified using high-performance liquid chromatography (HPLC). These methods could function to simplify the generation of thioether-tethered cyclic peptides due to the use of the thio-ene/yne click chemistry that possesses superior functional group tolerance and good yield. The introduction of thioether bonds into peptides takes advantage of the nucleophilic nature of cysteine residues and is redox-inert relative to disulfide bonds.

We present a protocol for the construction of thioether/vinyl sulfide-tethered helical peptides using photo-induced thiol-ene/thiol-yne hydrothiolation.

利用光致硫醇-烯/yne Hydrothiolation 构造硫醚类/乙烯基硫化物栓系螺旋肽

Here, we describe a detailed protocol for the preparation of thioether-tethered peptides using on-resin intramolecular/intermolecular thiol-ene ...

Microfluidic Preparation of Liquid Crystalline Elastomer Actuators

This paper focuses on the microfluidic process (and its parameters) to prepare actuating particles from liquid crystalline elastomers. The preparation usually consists in the formation of droplets containing low molar mass liquid crystals at elevated temperatures. Subsequently, these particle precursors are oriented in the flow field of the capillary and solidified by a crosslinking polymerization, which produces the final actuating particles. The optimization of the process is necessary to obtain the actuating particles and the proper variation of the process parameters (temperature and flow rate) and allows variations of size and shape (from oblate to strongly prolate morphologies) as well as the magnitude of actuation. In addition, it is possible to vary the type of actuation from elongation to contraction depending on the director profile induced to the droplets during the flow in the capillary, which again depends on the microfluidic process and its parameters. Furthermore, particles of more complex shapes, like core-shell structures or Janus particles, can be prepared by adjusting the setup. By the variation of the chemical structure and the mode of crosslinking (solidification) of the liquid crystalline elastomer, it is also possible to prepare actuating particles triggered by heat or UV-vis irradiation.

This article describes the microfluidic process and parameters to prepare actuating particles from liquid crystalline elastomers. This process allows the preparation of actuating particles and the variation of their size and shape (from oblate to strongly prolate, core-shell, and Janus morphologies) as well as the magnitude of actuation.

液晶弹性体致动器的微流控制备

This paper focuses on the microfluidic process (and its parameters) to prepare actuating particles from liquid crystalline elastomers. The preparation ...

Synthesis of Soft Polysiloxane-urea Elastomers for Intraocular Lens Application

This study discusses a synthesis route for soft polysiloxane-based urea (PSU) elastomers for their applications as accommodating intraocular lenses (a-IOLs). Aminopropyl-terminated polydimethylsiloxanes (PDMS) were previously prepared via the ring-chain equilibration of the cyclic siloxane octamethylcyclotetrasiloxane (D4) and 1,3-bis(3-aminopropyl)-tetramethyldisiloxane (APTMDS). Phenyl groups were introduced into the siloxane backbone via the copolymerization of D4 and 2,4,6,8-tetramethyl-2,4,6,8-tetraphenyl-cyclotetrasiloxane (D4Me,Ph). These polydimethyl-methyl-phenyl-siloxane-block copolymers were synthesized for increasing the refractive indices of polysiloxanes. For applications as an a-IOL, the refractive index of the polysiloxanes must be equivalent to that of a young human eye lens. The polysiloxane molecular weight is controlled by the ratio of the cyclic siloxane to the endblocker APTMDS. The transparency of the PSU elastomers is examined by the transmittance measurement of films between 200 and 750 nm, using a UV-Vis spectrophotometer. Transmittance values at 750 nm (upper end of the visible spectrum) are plotted against the PDMS molecular weight, and &#62; 90% of the transmittance is observed until a molecular weight of 18,000 g&#183;mol&#8722;1. Mechanical properties of the PSU elastomers are investigated using stress-strain tests on die-cut dog-bone-shaped specimens. For evaluating mechanical stability, mechanical hysteresis is measured by repeatedly stretching (10x) the specimens to 5% and 100% elongation. Hysteresis considerably decreases with the increase in the PDMS molecular weight. In vitro cytotoxicity of some selected PSU elastomers is evaluated using an MTS cell viability assay. The methods described herein permit the synthesis of a soft, transparent, and noncytotoxic PSU elastomer with a refractive index approximately equal to that of a young human eye lens.

This study describes synthetic routes for aminopropyl-terminated polydimethylsiloxanes and polydimethyl-methyl-phenyl-siloxane-block copolymers and for soft polysiloxane-based urea (PSU) elastomers. It presents the application of PSUs as accommodating an intraocular lens. An evaluation method for in vitro cytotoxicity is also described.

软聚聚硅氧烷-尿素弹性体在人工晶体中的应用

This study discusses a synthesis route for soft polysiloxane-based urea (PSU) elastomers for their applications as accommodating intraocular lenses ...

Synthesis of Monodisperse Cylindrical Nanoparticles via Crystallization-driven Self-assembly of Biodegradable Block Copolymers

The production of monodisperse cylindrical micelles is a significant challenge in polymer chemistry. Most cylindrical constructs formed from diblock copolymers are produced by one of three techniques: thin film rehydration, solvent switching or polymerization-induced self-assembly, and produce only flexible, polydisperse cylinders. Crystallization-driven self-assembly (CDSA) is a method which can produce cylinders with these properties, by stabilizing structures of a lower curvature due to the formation of a crystalline core. However, the living polymerization techniques by which most core-forming blocks are formed are not trivial processes and the CDSA process may yield unsatisfactory results if carried out incorrectly. Here, the synthesis of cylindrical nanoparticles from simple reagents is shown. The drying and purification of reagents prior to a ring-opening polymerization of &#949;-caprolactone catalyzed by diphenyl phosphate is described. This polymer is then chain extended by methyl methacrylate (MMA) followed by N,N-dimethyl acrylamide (DMA) using reversible addition&#8722;fragmentation chain-transfer (RAFT) polymerization, affording a triblock copolymer that can undergo CDSA in ethanol. The living CDSA process is outlined, the results of which yield cylindrical nanoparticles up to 500 nm in length and a length dispersity as low as 1.05. It is anticipated that these protocols will allow others to produce cylindrical nanostructures and elevate the field of CDSA in the future.

Crystallization-driven self-assembly (CDSA) displays the unique ability to fabricate cylindrical nanostructures of narrow length distributions. The organocatalyzed ring-opening polymerization of &#949;-caprolactone and subsequent chain extensions of methyl methacrylate and N,N-dimethyl acrylamide are demonstrated. A living CDSA protocol that produces monodisperse cylinders up to 500 nm in length is outlined.

通过结晶驱动生物降解块共聚物的自组装合成单分散圆柱状纳米粒子

The production of monodisperse cylindrical micelles is a significant challenge in polymer chemistry. Most cylindrical constructs formed from diblock ...

Preparation of Monodomain Liquid Crystal Elastomers and Liquid Crystal Elastomer Nanocomposites

LCEs are shape-responsive materials with fully reversible shape change and potential applications in medicine, tissue engineering, artificial muscles, and as soft robots. Here, we demonstrate the preparation of shape-responsive liquid crystal elastomers (LCEs) and LCE nanocomposites along with characterization of their shape-responsiveness, mechanical properties, and microstructure. Two types of LCEs &#8212; polysiloxane-based and epoxy-based &#8212; are synthesized, aligned, and characterized. Polysiloxane-based LCEs are prepared through two crosslinking steps, the second under an applied load, resulting in monodomain LCEs. Polysiloxane LCE nanocomposites are prepared through the addition of conductive carbon black nanoparticles, both throughout the bulk of the LCE and to the LCE surface. Epoxy-based LCEs are prepared through a reversible esterification reaction. Epoxy-based LCEs are aligned through the application of a uniaxial load at elevated (160 &#176;C) temperatures. Aligned LCEs and LCE nanocomposites are characterized with respect to reversible strain, mechanical stiffness, and liquid crystal ordering using a combination of imaging, two-dimensional X-ray diffraction measurements, differential scanning calorimetry, and dynamic mechanical analysis. LCEs and LCE nanocomposites can be stimulated with heat and/or electrical potential to controllably generate strains in cell culture media, and we demonstrate the application of LCEs as shape-responsive substrates for cell culture using a custom-made apparatus.

We demonstrate the preparation of siloxane-based and epoxy-based liquid crystal elastomers (LCEs) and LCE nanocomposites. The LCEs are characterized with respect to reversible strain, liquid crystal ordering, and stiffness. As a potential application, we demonstrate their use as shape-responsive substrates in a custom device for active cell culture.

单域液晶的弹性体和液晶橡胶纳米复合材料的制备

LCEs are shape-responsive materials with fully reversible shape change and potential applications in medicine, tissue engineering, artificial muscles, and ...

生物工程

Fabricating Degradable Thermoresponsive Hydrogels on Multiple Length Scales via Reactive Extrusion, Microfluidics, Self-assembly, and Electrospinning

While various smart materials have been explored for a variety of biomedical applications (e.g., drug delivery, tissue engineering, bioimaging, etc.), their ultimate clinical use has been hampered by the lack of biologically-relevant degradation observed for most smart materials. This is particularly true for temperature-responsive hydrogels, which are almost uniformly based on polymers that are functionally non-degradable (e.g., poly(N-isopropylacrylamide) (PNIPAM) or poly(oligoethylene glycol methacrylate) (POEGMA)). As such, to effectively translate the potential of thermoresponsive hydrogels to the challenges of remote-controlled or metabolism-regulated drug delivery, cell scaffolds with tunable cell-material interactions, theranostic materials with the potential for both imaging and drug delivery, and other such applications, a method is required to render the hydrogels (if not fully degradable) at least capable of renal clearance following the required lifetime of the material. To that end, this protocol describes the preparation of hydrolytically-degradable hydrazone-crosslinked hydrogels on multiple length scales based on the reaction between hydrazide and aldehyde-functionalized PNIPAM or POEGMA oligomers with molecular weights below the renal filtration limit. Specifically, methods to fabricate degradable thermoresponsive bulk hydrogels (using a double barrel syringe technique), hydrogel particles (on both the microscale through the use of a microfluidics platform facilitating simultaneous mixing and emulsification of the precursor polymers and the nanoscale through the use of a thermally-driven self-assembly and cross-linking method), and hydrogel nanofibers (using a reactive electrospinning strategy) are described. In each case, hydrogels with temperature-responsive properties similar to those achieved via conventional free radical cross-linking processes can be achieved, but the hydrazone cross-linked network can be degraded over time to re-form the oligomeric precursor polymers and enable clearance. As such, we anticipate these methods (which may be generically applied to any synthetic water-soluble polymer, not just smart materials) will enable easier translation of synthetic smart materials to clinical applications.

Protocols are described for the fabrication of degradable thermoresponsive hydrogels based on hydrazone cross-linking of polymeric oligomers on the bulk scale, microscale, and nanoscale, the latter for preparation of both gel nanoparticles and nanofibers.

通过反应挤出、微流体、自组装和电纺丝制备多长尺度可降解 Thermoresponsive 水凝胶

While various smart materials have been explored for a variety of biomedical applications (e.g., drug delivery, tissue engineering, bioimaging, etc.), ...

Synthesis of Biocompatible Liquid Crystal Elastomer Foams as Cell Scaffolds for 3D Spatial Cell Cultures

Here, we present a step-by-step preparation of a 3D, biodegradable, foam-like cell scaffold. These scaffolds were prepared by cross-linking star block co-polymers featuring cholesterol units as side-chain pendant groups, resulting in smectic-A (SmA) liquid crystal elastomers (LCEs). Foam-like scaffolds, prepared using metal templates, feature interconnected microchannels, making them suitable as 3D cell culture scaffolds. The combined properties of the regular structure of the metal foam and of the elastomer result in a 3D cell scaffold that promotes not only higher cell proliferation compared to conventional porous templated films, but also better management of mass transport (i.e., nutrients, gases, waste, etc.). The nature of the metal template allows for the easy manipulation of foam shapes (i.e., rolls or films) and for the preparation of scaffolds of different pore sizes for different cell studies while preserving the interconnected porous nature of the template. The etching process does not affect the chemistry of the elastomers, preserving their biocompatible and biodegradable nature. We show that these smectic LCEs, when grown for extensive time periods, enable the study of clinically relevant and complex tissue constructs while promoting the growth and proliferation of cells.

This study presents a methodology to prepare 3D, biodegradable, foam-like cell scaffolds based on biocompatible side-chain liquid crystal elastomers (LCEs). Confocal microscopy experiments show that foam-like LCEs allow for cell attachment, proliferation, and the spontaneous alignment of C2C12s myoblasts.

生物相容的液晶弹性体泡沫的合成中用作细胞支架的三维空间细胞培养

Here, we present a step-by-step preparation of a 3D, biodegradable, foam-like cell scaffold. These scaffolds were prepared by cross-linking star block ...