Simultaneous in-situ Construction of Hybrid
Films by Photoreaction1
Bo Yuan, Jianwen Yang*, and Zhaohua Zeng*
Instituite of Polymer Science, School of Chemistry & Chemical Engineering, Sun Yat-sen University GuangZhou 510275
Abstract
Organic/inorganic materials based on nano-titania have received more and more attention
due to their attractive optical properties, balanced mechanical performance and facile processing.
Triarylsulfonium salt was used for trigging free radical polymerization of acrylates and producing
super protonic acid to control the hydrolysis and condensation of TBT. By means of FT-IR monitoring,
it was confirmed that the organic networks and inorganic nano-particles were formed almost
simultaneously with some mutual interaction. The formation and morphology of the titania particles
could be controlled by extending pre-exposure to moisture and retarding the free radical
photopolymerization of acrylates. XPS analysis indicated that moisture pre-exposure was favorable for
improving the titania content in the surface layer of UV-cured film.
Key words: Organic/inorganic hybrid, sol-gel, in-situ reaction, photopolymerization, nano-titania
Introduction
Since the late 1980s, molecular level combination between organic polymers and inorganic
materialshas been of great interest，they are termed “organic/inorganic hybrid materials”
Up to now, there are only very few literatures reported on the preparation of UV curable
polymer/titania hybrid materials by sol-gel method. This may be due to that the precursor titanium
tetraalkoxide is very reactive and direct hydrolysis usually leads to precipitates. The common strategy
for dealing with this problem includes chemical modification of titanium alkoxide and confinement of
water in reverse micelles. Wan et al. prepared UV curable acrylic resin/titania organic/inorganic hybrid
films by controlled hydrolysis of titanium tetrabutoxide in Span 85/Tween 80 reverse micelles and
subsequent in-situ photopolymerization of acrylic monomers. Soucek described the application of
sulfonium salt in the in-situ preparation of polyepoxide/titania hybrid film by UV-irradiation, whereas
the SAXS determination of cured film did not give positive evidence supporting the formation of
titania particle from titanium alkoxide.
In this work, sulfonium salt and photoinitiator TPO were utilized to produce protonic acid and
active free radical by UV-irradiation, respectively. Moisture pre-exposure and TEMPO-retarded
photopolymerization of acrylates were designed to cooperatively control the formation of inorganic
particles and organic network.
Experimental
1
中山大学化学与化学工程学院第六届创新化学实验与研究基金项目（批准号：200626）
第一作者：袁波（1984 年出生）
，女，中山大学化学与化学工程专业应用化学系 2002 级
指导教师：杨建文，曾兆华 Email：cesyjw@mail.sysu.edu.cn
150
Photoinitiators were dissolved in the mixture of EB600 and HEMA (weight ratio of EB600 to
HEMA is 6/4) under ultrasonic, which was then blended with TBT under thoroughly stirring at ambient
temperature to form a transparent mixture. The mixture was filled into a designed PET cell with
thickness of 280 m and then installed in a humid cabinet (RH 82 %) with a quartz window. The UV
irradiation source is 125W medium pressure mercury lamp (Philip, Holland) with high UV output
efficiency. In an effort to identify an optimal method for controlling the morphology of the cured
hybrid films, several processing methods were evaluated: A. Instantly UV-irradiation as soon as the
wet film conveyed into the humid cabinet. B. Exposed to moisture in humid cabinet for 90min after
UV-irradiation. C. UV-irradiation after the wet film exposed to moisture in the cabinet for a controlled
period (5, 15 30 min, respectively). The naming system is shown below:
Results and discussions
Synthesis of the in-situ hybrid cured films
The
dual
photoreactions,
were
proposed
for
the
blend
of
epoxy
acrylate/HEMA/TBT/triarylsulfonium salt as soon as the wet film effectively exposed to UV irradiation
(Scheme 1). As Scheme 1 showed, firstly, the photo-released free radical could be exploited to
construct organic network by initiating free radical polymerization of acrylates, which suppresses the
congregation of formed titania particles. This is proved by the decreasing absorption band at 1634cm-1
which is assigned to the acryloxyl groups(Figure 1a). Secondly, The protonic acid can be utilized to
slow down the hydrolysis and polycondensation, and control the formation of metal oxide particles. As
Figure 1 showed, The Ti-O-Ti structure contained in the produced titanium dioxide and/or
titanium-oxo-clusters could be diagnosed by the emergence of absorption band at 763 cm-1, it thus
could be confirmed that the titania or titanium-oxo-clusters were formed with UV irradiation and
moisture exposure. Therefore, the FT-IR spectra additionally indicate that the organic network and
inorganic phase has been quickly formed almost at the same time.
OBu
BuO Ti OBu
H2 O/hydrolysis
OBu
BuO Ti OH
H+
OBu
triarysulfonium salt
O
O C CH CH2
Scheme 1
OBu
OBu
condensation
H+
BuO Ti
OBu
OBu
O Ti OBu
Titanium dioxide
OBu
UV irradiation
R
Free radical polymerization
Organic network
Dual photoreactions for TBT hydrolysis and acrylates polymerization
151
(a)
C=C
-1
1634cm
Absorbance
irradiation time
240s
160s
100s
40s
0s
1800
1760
1720
1680
Wavenumbers / cm-1
1640
1600
Figure 1 FT-IR spectra for S5-TBT30 hybrid sample during UV irradiation (a)1700~1600 cm-1 (b) 1250~400 cm-1
Morphology of the in-situ hybrid cured films
Scanning electron microscopy (SEM) was performed to investigate the morphology of UV-cured
hybrid films. The microphotographs are shown in Figure 2. In Figure 2a, the film was cured so quickly
that TBT hydrolysis was suppressed by the instantly formed organic network and the quickly
photo-released acid. And It was suggested that the photopolymerization rate of organic component have
significant affects on the morphology of the inorganic particles, figure 2b and c should be an evidence
for controlling the nano-morphology of titania particles while in-situ forming titania-organic hybrid
films.
Moisture may be favorable to TBT hydrolysis and formation of titania particles. Fast UV-curing
will severely suppress the formation of titania particle due to limitation of moisture diffusion and
alcohol removal. The proposal seems to be supported with the SEM observations of cured hybrid films.
The inorganic particles in cured films grew up with moisture pre-exposure extending by comparing
Figure 2d, e, f and g mutually.
The sample without TPO, as shown in Figure 2d, photocrosslinked in low rate and small particles
dispersed hybrid film produced. For the film pre-exposed to moisture for 30 min (Figure 2g), serious
titania congregation occurred and large ununiform inorganic particles were resulted due to excessive
up-taking of moisture and serious hydrolysis in the absence of acid anti-catalyst. Short pre-exposure
time facilitated to form small and uniform titania particles as shown in Figure 2e, f. It means that the
formation and morphology of titania nano-particles in curing hybrid films could be controlled by
moisture pre-exposure of wet films.
152
Figure 2
SEM micrographs of hybrid films
(a) S5T1-TBT30-A2; (b)S5T1-TEM0.3-TBT30-A4; (c)S5T1-TEM0.6-TBT30-A10; (d)S5-TBT30-A6; (e)
S5-TBT30-C5(UV for 6min); (f) S5-TBT30-C15(UV for 6min); (g) S5-TBT30-C30(UV for 6min);
153
XPS analysis of the in-situ hybrid cured films
XPS was employed to investigate the chemical environment of some specific atoms. The binding
energy of specific atom in compounds is variable with its chemical bonding status and exclusively
shifts with related chemical reaction. Figure 3 shows the binding energy of Ti2p in the cured hybrid
films prepared by different procedures. For the sample S5-TBT-30-C30 exposed to moisture for 30 min
before UV irradiation, the corresponding Ti2p peaks located at 458.80 eV which is very close to the
reported Ti2p peak (458.1 eV) for titanium dioxide. It could be concluded that pre-exposure or
post-exposure to moisture could enhance the formation of titanium dioxide, but the former seems to be
more efficient for controlling the formation of titania.
14000
458.80
S5-TBT30-C30
12000
459.05
S5-TBT30-B90
Counts / s
10000
8000
459.30
S5-TBT30-A6
6000
4000
2000
470
465
460
455
450
Binding energy / eV
Figure 3 XPS spectra of Ti2p in the hybrid cured films
prepared by different method
Conclusion
1. Titania based hybrid films were prepared by the dual effect photoreaction and an in-situ
sol-gel reaction. Triarylsulfonium salt, was used for trigging free radical polymerization of acrylates
and producing super protonic acid to control TBT transformation to titania nano-particle. It was
confirmed by FT-IR that the organic networks and inorganic nanoparticles were formed almost
simultaneously with some mutual interaction.
2. The formation and morphology of the titania particles could be controlled by extending
pre-exposure to moisture and the free radical photopolymerization of acrylates.
3. XPS analysis indicated that moisture pre-exposure was favorable for increasing the
titania content in the surface layer of UV-cured film.
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含二氧化钛有机/无机杂化体系的光固化同时原
位构筑
袁波 杨建文* 曾兆华*
中山大学化学与化学工程学院高分子所 广州 510275
摘要
纳米二氧化钛有机/无机杂化材料因其突出的光学性能、平衡的力学性能及易加工成型等
特点而渐受关注。本论文提出利用芳基硫鎓盐光解产生活性自由基和质子酸的特点，分别引发有
机体系的自由基聚合和原位控制 TBT 水解-缩合反应，固化过程的红外光谱跟踪研究表明，有机
交联网络与二氧化钛纳米粒子几乎同时形成。创新性地通过潮气前处理和延缓自由基聚合等手
段，成功实现对固化膜中无机粒子的形态进行有效控制。XPS 分析结果表明经过潮气前处理更有
利于生成较多的二氧化钛颗粒。
关键词：有机/无机杂化，溶胶-凝胶，原位聚合，光聚合，纳米二氧化钛
致 谢
在我的指导老师杨建文副教授和曾兆华副教授以及师姐张夏虹博士的悉心指导与亲切
关怀下，我终于完成了这篇论文。他们严谨踏实又富于创新精神的研究态度以及实事求是、
孜孜以求的为人精神对我影响甚深，令我终身难忘，受益非浅。在此，谨向两位老师和带领
我完成实验的师姐表示最衷心的感谢和崇高的敬意！在整个论文完成过程中，还得到了本实
验室黄亮师兄、陈嘉师姐、胡雅琴师姐、杨金师兄以及其他师兄师姐和同学多方面的帮助。
特此向他们表示最诚挚的谢意！衷心感谢我的父母和亲人在生活上无微不至地关怀和精神上
的鼓励，这是我完成学业的强大精神动力和坚强后盾。感谢四年来关心和支持我的同学和朋
友们！
袁波
2006 年 6 月于中山大学
155
156