Department of Molecular and Macromolecular Chemistry, Graduate School of Engineering , Nagoya University , Furo-cho, Chikusa-ku, Nagoya 464-8603 , Japan.
Biomacromolecules. 2019 Jan 14;20(1):192-203. doi: 10.1021/acs.biomac.8b01298. Epub 2018 Oct 25.
A series of cinnamic monomers, which can be derived from naturally occurring phenylpropanoids, were radically copolymerized with vinyl monomers such as methyl acrylate (MA) and styrene (St). Although the monomer reactivity ratios were close to zero for all the cinnamic monomers, such as methyl cinnamate (CAMe), cinnamic acid (CA), N-isopropyl cinnamide (CNIPAm), cinnamaldehyde (CAld), and cinnamonitrile (CN), they were incorporated into the copolymers and significantly increased the glass transition temperatures despite the relatively low incorporation rates of up to 40 mol % due to their rigid 1,2-disubstituted structures. The regioselectivity of the radical copolymerization of CAMe was evaluated on the basis of the results of ruthenium-catalyzed atom transfer radical additions as model reactions. The obtained products suggest that the radicals of MA and St predominantly attack the vinyl carbon of the carbonyl side of CAMe and that the propagation of CAMe mainly occurs via the styrenic radical. The ruthenium-catalyzed living radical polymerization, nitroxide-mediated polymerization (NMP), and reversible addition-fragmentation chain transfer (RAFT) polymerization provided the copolymers with controlled molecular weights, narrow molecular weight distributions, and controlled comonomer compositions. The copolymers of N-isopropylacrylamide (NIPAM) and CNIPAm prepared via RAFT copolymerization showed thermoresponsivity with a lower critical solution temperature (LCST) that could be tuned by altering the comonomer incorporation and a higher LCST than the copolymers of NIPAM and St, which possessed similar molecular weights and similar NIPAM contents, due to the additional N-isopropylamide groups in the CNIPAm units compared to the St units.
一系列肉桂单体可以从天然存在的苯丙素衍生而来，与乙烯基单体如甲基丙烯酸甲酯（MA）和苯乙烯（St）进行自由基共聚。尽管所有肉桂单体的单体反应性比都接近零，如肉桂酸甲酯（CAMe）、肉桂酸（CA）、N-异丙基肉桂酰胺（CNIPAm）、肉桂醛（CAld）和肉桂腈（CN），它们仍被掺入共聚物中，并显著提高玻璃化转变温度，尽管由于其刚性的 1,2-二取代结构，掺入率相对较低，最高可达 40mol%。基于钌催化原子转移自由基加成反应的结果，评估了 CAMe 的自由基共聚的区域选择性作为模型反应。得到的产物表明，MA 和 St 的自由基主要攻击 CAMe 羰基侧的乙烯基碳，CAMe 的聚合主要通过苯乙烯自由基进行。钌催化的活性自由基聚合、氮氧自由基介导的聚合（NMP）和可逆加成-断裂链转移（RAFT）聚合为共聚物提供了可控的分子量、较窄的分子量分布和可控的共聚单体组成。通过 RAFT 共聚制备的 N-异丙基丙烯酰胺（NIPAM）和 CNIPAm 的共聚物具有热响应性，其低临界溶液温度（LCST）可以通过改变共聚单体的掺入量进行调节，并且比具有相似分子量和相似 NIPAM 含量的 NIPAM 和 St 的共聚物的 LCST 更高，这是由于 CNIPAm 单元中的额外的 N-异丙基酰胺基团与 St 单元相比。
