Azobisisobutyronitrile (AIBN, structure as follows) can initiate the free radical polymerization of styrene to polystyrene (PS):

<MultiModal>![Styrene polymerization initiated by AIBN: `CC(C)(C#N)/N=N/C(C)(C#N)C` under heating conditions](/media/uploads/83cac3e8-d96e-4d0e-85e0-7d015b895e4d.png)</MultiModal>

Polymerization initiated by $^{14}C$-labeled AIBN yields PS with a (number average) molecular weight of $1.30 \times 10^6$. Scintillation counter measurements show that the AIBN radioactivity is $1. 919 \times 10^8 counts· min^{-1}·mol^{-1}$; the radioactivity of $5.80g$ PS is $858 counts·min^{-1}$.

The following statements are made:

1. AIBN heating initiates polymerization and requires the release of one molecule of gas.

2. Each molecule of the polymer has one cyano group.

3. The polymer may have a center of symmetry.

4. Each molecule of AIBN can produce two molecules of polymer.

The option below containing all correct statements is:
用偶氮二异丁腈(AIBN,结构如下)可引发苯乙烯聚合为聚苯乙烯(PS)的自由基聚合反应

<MultiModal>![苯乙烯在加热条件下由AIBN：`CC(C)(C#N)/N=N/C(C)(C#N)C`引发聚合](/media/uploads/83cac3e8-d96e-4d0e-85e0-7d015b895e4d.png)</MultiModal>

用$^{14}C$标记的AIBN引发聚合得到(数均)分子量为$1.30 \times 10^6$的PS。闪烁计数器测定表明，AIBN放射活性为 $1. 919 \times 10^8 counts· min^{-1}·mol^{-1}$；$5.80g$ PS放射活性为$858 counts·min^{-1}$。

有以下说法：

1.AIBN加热引发聚合需要放出一分子气体

2.每分子该聚合物具有一个氰基

3.该聚合物可能具有对称中心

4.每分子AIBN可以产生两分子聚合物

以下选项包含全部正确说法的是：
All statements are incorrect.
1
2
3
4
1,2
1,3
1,4
2,3
2,4
3,4
1,2,3
1,2,4
2,3,4
1,3,4
1,2,3,4
所有说法均不正确
1
2
3
4
1,2
1,3
1,4
2,3
2,4
3,4
1,2,3
1,2,4
2,3,4
1,3,4
1,2,3,4
AIBN undergoes homolytic cleavage upon heating, generating two 2-cyano-2-propyl radicals: `C[C](C#N)C` (the radical is located on the central carbon), and releasing one molecule of nitrogen gas.

<Checkpoint>[AIBN heating initiates polymerization and requires the release of one molecule of nitrogen gas, statement 1 is correct](1)</Checkpoint>

Subsequently, the radical reacts with styrene, generating a radical at the α-position of the phenyl group to initiate polymerization.

The number of styrene monomers contained in each PS chain is: $1.30 \times 10^6  \div 104.1 = 1.25 \times 10^4$.
The number of styrene monomers corresponding to each AIBN is: $1.919 \times 10^8 \div [858 \div (5.80 \div 104.1)] = 1.24 \times 10^4$.
The two values are close; since one AIBN molecule generates two radicals, the chain termination method under experimental conditions is coupling termination. One molecule of AIBN produces one molecule of polymer.

<Checkpoint>[The chain termination method under experimental conditions is coupling termination. One molecule of AIBN produces one molecule of polymer, statement 4 is incorrect](1)</Checkpoint>

<Checkpoint>[Calculated number of styrene monomers contained in each PS chain is $1.25 \times 10^4$, the number of styrene monomers corresponding to each AIBN is: $1.24 \times 10^4$](1)</Checkpoint>

Then it is easy to obtain the final polymer structure as:

<MultiModal>![The basic structure of the polymer is: `CC(CC(C(C1=CC=CC=C1)CC(C)(C#N)C)C2=CC=CC=C2)(C#N)C` (both degrees of polymerization x and y are 1), both repeating units are `[*]CC([*])C1=CC=CC=C1` ([*] indicates that the repeating unit is bonded to other parts of the polymer)](/media/uploads/7311c81a-8dbd-4d0f-bbed-5d437740cfb5.png)</MultiModal>

As can be seen from the structure, each molecule of this polymer has 2 cyano groups.

<Checkpoint>[The molecule of this polymer has 2 cyano groups, statement 2 is incorrect](1)</Checkpoint>

When the degrees of polymerization of the two segments are the same, i.e., x=y, the polymer has a center of symmetry.

<Checkpoint>[When the degree of polymerization x=y, the polymer has a center of symmetry, statement 3 is correct](1)</Checkpoint>

Statements 1 and 3 are correct, choose G
AIBN受热均裂，生成两个2-氰基-2-丙基自由基：`C[C](C#N)C`（自由基位于中心的碳上），并放出一分子氮气。

<Checkpoint>[AIBN加热引发聚合需要放出一分子氮气，说法1正确](1)</Checkpoint>

随后该自由基与苯乙烯反应，在苯基α位产生自由基引发聚合。

每根PS链含有的苯乙烯单体数目为：$1.30 \times 10^6  \div 104.1 = 1.25 \times 10^4$。
每个 AIBN 对应的苯乙烯单体数目为：$1.919 \times 10^8 \div [858 \div (5.80 \div 104.1)] = 1.24 \times 10^4$。
二者数值相近；由于1个AIBN分子产生2个自由基，因此实验条件下链终止的方式是偶合终止。每分子AIBN产生一分子聚合物。

<Checkpoint>[实验条件下链终止的方式是偶合终止。每分子AIBN产生一分子聚合物，说法4错误](1)</Checkpoint>

<Checkpoint>[计算得每根PS链含有的苯乙烯单体数目为$1.25 \times 10^4$，每个 AIBN 对应的苯乙烯单体数目为：$1.24 \times 10^4$](1)</Checkpoint>

则容易得到最终聚合物的结构为：

<MultiModal>![聚合物的基本结构为：`CC(CC(C(C1=CC=CC=C1)CC(C)(C#N)C)C2=CC=CC=C2)(C#N)C`（两段聚合度x, y均为1），两段重复单元均为`[*]CC([*])C1=CC=CC=C1`（[*]表示重复单元与聚合物其他部分成键）](/media/uploads/7311c81a-8dbd-4d0f-bbed-5d437740cfb5.png)</MultiModal>

由结构可知，每分子该聚合物具有2个氰基。

<Checkpoint>[分子该聚合物具有2个氰基，说法2错误](1)</Checkpoint>

当两段聚合物聚合度相同时，即x=y时，该聚合物具有对称中心。

<Checkpoint>[当聚合度x=y时，该聚合物具有对称中心，说法3正确](1)</Checkpoint>

说法1，3正确，选G