三氟氯乙烯与甲基异丙烯基醚的光诱导共聚反应★

doi:10.6023/A23080387

摘要/Abstract

氟聚合物综合性能优异, 在诸多领域发挥了重要作用. 三氟氯乙烯(chlorotrifluoroethylene, CTFE)与乙烯基醚共聚物被用于高性能涂料, 但其较低的玻璃化转变温度对应用场景带来了局限. 在本工作中, 发展了CTFE与甲基异丙烯基醚(methyl isopropenyl ether, MIE)的光照自由基共聚反应, 在室温常压条件下合成了全新化学结构的氟烯烃与烯基醚共聚物. 聚合反应过程符合一级动力学与交替共聚特征, 通过控制链转移剂用量与MIE转化率可合成不同分子量的共聚物, 表明该聚合反应具备一定的可控性, 但共聚物分子量分布较宽、链末端保真度有限. 在此基础上, 本工作首次揭示了CTFE-MIE共聚物比CTFE-乙烯基乙醚共聚物的玻璃化转变温度提高了近50 ℃, 有助于进一步开发高性能氟聚合物材料.

关键词: 氟聚合物, 共聚物, 光照聚合, 可逆失活自由基聚合, 三氟氯乙烯

Fluoropolymers exhibit unique properties, such as outstanding thermal stability and chemical inertness, ultralow surface energy, and have found broad applications in lots of areas. Many fluoropolymers show high crystallinity and low solubility, restricting their practical usage through melting and solution processing. To address such issues, copolymerization of fluoroalkenes and comonomers have been developed to prepare fluorinated copolymers that retain fluoroalkyl characteristics and good processibility, bringing many important commercial products, for example, copolymers of chlorotrifluoroethylene (CTFE) and vinyl ethers. However, such copolymers could possess low glass transition temperature (T_g), which is a key property to influence the applicable scope. In this work, we report copolymerization of CTFE and methyl isopropenyl ether (MIE) for the first time, which have enabled the synthesis of novel fluorinated copolymers under LED (light emitting diode) light irradiation conditions by merging an organic thermally activated delayed fluorescence catalyst and a redox active organic amine via a redox-relay catalysis. In comparison to conventional free radical (co)polymerization of fluoroalkenes, this method not only provides main-chain fluoropolymers of readily tunable molecular weights as evidenced by gel permeation chromatography (GPC) and multi-angle light scattering detection coupled with GPC (GPC-MALS), but also allows smooth transformation of fluoroalkene feedstock at ambient pressure using common Schlenk glassware without needing high-pressure metallic vessels. Although the obtained CTFE-MIE copolymers exhibited less controlled molecular weight distributions (MWDs) and limited chain-end fidelity as confirmed by chain-extension polymerization and GPC analysis, the chain-growth process presents first-order kinetics as validated by monitoring the monomer consumption, and follows alternating copolymerization as supported by the variation of degrees of polymerization (DPs) of both vinyl compounds along the light irradiation time, presenting improved chain-growth control as compared to conventional free radical transformation. Notably, as analyzed by differential scanning calorimetry (DSC), in contrast to copolymers of CTFE and ethyl vinyl ether (EVE), the CTFE-MIE copolymers with similar molecular weights exhibit clearly improved T_g of about 50 ℃ via simply introducing methyl substituents on the polymer backbone. Given the broad interests in fluoropolymers and established applications of fluoroalkene-vinyl ether copolymers, we believe that this work should be informative to the rational design of novel fluoropolymers and attractive for material engineering with improved thermal stability.

Key words: fluoropolymer, copolymer, photopolymerization, reversible deactivation radical polymerization, chlorotrifluoroethylene

引用此文

易敬霖, 陈茂. 三氟氯乙烯与甲基异丙烯基醚的光诱导共聚反应^★[J]. 化学学报, 2024, 82(2): 126-131.

Jinglin Yi, Mao Chen. Photo-Induced Copolymerization of Chlorotrifluoroethylene and Methyl Isopropenyl Ether^★[J]. Acta Chimica Sinica, 2024, 82(2): 126-131.

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图/表 7

图1. (A) PMA与PMMA的化学结构及玻璃化转变温度; (B) 本文设计示意图

Figure 1. (A) Chemical structures of PMA and PMMA and their glass transition temperatures; (B) design in this study

图2. (A) CTFE与MIE的光照共聚反应示意图; (B) 光催化剂结构式; (C) 链转移剂结构式

Figure 2. (A) Photopolymerization of CTFE and MIE; (B) chemical structure of PC; (C) chemical structure of CTAs

Entry	CTA	Light source	Conv. (MIE)^b/%	M_n,GPC^c/kDa	Ð^c
1	1a	blue	85	10.7	2.11
2	1b	blue	80	9.9	1.96
3	1c	blue	20	4.4	2.13
4	2a	blue	90	8.3	1.96
5	2b	blue	85	5.6	1.64
6	2c	blue	76	5.9	1.57
7	3c	blue	<5	—	—
8	4c	blue	83	8.6	2.02
9	5c	blue	<5	—	—
10	2c	—	0	—	—
11	2c	purple	79	5.3	1.64
12	2c	white	52	3.4	1.53
13^d	2c	white	<5	—	—

表1. 优化CTFE与MIE光照共聚反应条件a

Table 1. Optimization of reaction conditions for the copolymerization of CTFE and MIE under light irradiationa

Entry	[CTFE]/[MIE]/[CTA]	Conv. (MIE)^b/%	M_n,GPC^c/kDa	M_n,MALS^d/kDa	Ð^c
1	400/200/1	>99	19.1		1.77
2	400/300/1	83	16.2		1.75
3	800/400/1	>99	24.8	87.5	1.85
4	1000/500/1	>99	34.8	212.8	1.90

表2. 合成不同分子量的CTFE与MIE共聚物a

Table 2. Synthesis of CTFE-MIE copolymers with different molecular weightsa

图3. (A) 聚合度与光照时间的关系图, CTFE(空心点), MIE(实心点); (B) ln([M]0/[M]t)与光照时间的关系图, [M]0和[M]t分别为时间点0和t时, MIE的摩尔浓度; (C) 分子量(实心点)及其分布(空心点)随MIE转化率变化的示意图

Figure 3. (A) DPs of CTFE (empty symbols) and MIE (filled symbols) vs. exposure time; (B) ln([M]0/[M]t) vs. exposure time. [M]0 and [M]t are the concentrations of MIE at time points 0 and t, respectively; (C) Mn (filled symbols) and ? (empty symbols) vs. MIE conversion (%)

图4. 扩链反应制备含氟嵌段共聚物的GPC表征结果. P1=P(CTFE-alt-MIE), P1a=P(CTFE-alt-MIE)-b-PMMA, P1b=P(CTFE- alt-MIE)-b-PVAc

Figure 4. GPC results of fluorinated block copolymers synthesized via chain extensions. P1=P(CTFE-alt-MIE), P1a=P(CTFE-alt-MIE)- b-PMMA, P1b=P(CTFE-alt-MIE)-b-PVAc

图5. CTFE-EVE共聚物(P2与P3)与CTFE-MIE共聚物(P4与P5)的DSC曲线

Figure 5. DSC profiles of CTFE-EVE copolymers (P2 and P3) and CTFE-MIE copolymers (P4 and P5)

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